Network for neutralizing the characteristic reactance of a loaded line.



R. S. HOYT. Q

NETWORK FOR NEUIRALIZING THE CHARAGTERISTIC REACTANCE bF A LGADED LINE.

APPLICATION FELED MN. 24. ms.

1,243,066. Patented Oct. 16, 191?.-

3 SHEETS-SHEET I. .11" .1 L3 f PM N M Inuentar: RqySHoyt D9?" attorney.

R. S. HOYT.

NETWORK FOR NEUTRAUZING THE GHARACTERISTIC REACTANCE OF A LOAQED LINE.

APPLICATION FILED JAN. 24 I916.

1,243,066Q Patented Oct. 16,1917.

Inventor: y 5 5 p r M Jzmm; l

R. S. HUYT.

NETWORK FOR NEUTRAUZING THE,CHARACTERISTIC REACTANCE OF A LOADED LINE. APPLICATION mm JAN. 24. i916.

1,243,066. Patented 00$. 16,1917.

Inventor Ray S. Hoyt per Jtiorney.

. .BJISHHSSIUI! line.

UNITED STATES PATENT OFFICE.

RAY S. HOYT, OF BROOKLYN, NEW YORK, ASSIGNOR TO AMERICAN TELEPHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

NETWORK FOB NEUTRALIZING THE CHARACTERISTIC REACTANCE OF A LOADED LINE.

Specification of Letters Patent.

Patented Oct. 16, 1917.

Application filed January 24, 1916. Serial No. 73,950.

T 0 all whom it may concern:

Be it known that I, RAY S. Horr, residing at Brooklyn, in the county of' Kings and State of New York, have invented certain Im rovements in Network for Neutralizing t e Characteristic Reactance of a Loaded Line, of which the following is a. specification.

M invention relates to a circuit arrange- "ient associated with a periodically loaded Said circuit arrangement; is hereinafter termed in accordance with common usage, a network. Its object is to provide a network having a purel reactive impedance substantially equal an opposite to the reactance component of the characteristic impedance of a periodically loaded line o'r'el' the range of frequencies necessary for the telephonic transmission of speech. A further object of my invention is by the cooperative combination of said network and said loaded line to provide a transmission system whose impedance is substantially that o a c ZlSttlllb non-inductive resistance over said ran e of frequencies.

It is a well known not that the uniform non-loaded transmission line has a char acteristic impedance which is substantially that of a pure non-inductive resistance over the range of telephonic frequencies. It is further known that the characteristic impedance of a periodically loaded line has a resistance component which is a function of the length. of the initial section. that is, the distance from the beginning of the line to the first load coil, and which in general varies greatly over the range of telephonic frequencies. Said characteristic impedance has also a reactance component which likewise varies with the length of initial section and also with the frequency. The impedance characteristics of the non-loaded line and. the periodically loaded line are, therefore, quite dissimilar." I

In telephony it 'is often desirable and necessary to connect a. periodically loaded line in series with a non-loaded line. Owing to the above-mentioned dissimilar impedance characteristics of said lines, a reflco tion of telephonic waves. with consequent energy loss and inferior transmission, re sults when said lines are connected directly in series for the telephonic transmission of speech. My intention contemplates p-rovid ing and prefixing to the loaded line a net work and choosing a particular length of initial. section of the loaded line whereby the charzu-teristic impedance of the combination is substantially that of a pure resistance over a preassigncd range of frequencies, preferably the range of frequencies necessary for the cllicicnt transmission of speech signals. W'hen this combination is connected in series with a non-loaded line, preferahlr through an autotranstormer, the impee'lancc characteristic of the arrangement. as seen from the sending end, is sub stantially that of a single continuous transmission linc.

My invention is best understood by reference to the accompanying drawings in which F gure l is a diagram illustrating the network: Fig. 3 is a diagram illustrating the network connected to a periodically loaded line; Fig. 3 is a diagram illustrating a non-loaded line connected through an auto transformer and the network of my inveu tion to a perimlirally loaded. line; Fig. l

line have in practice a negligible cfl'ect on the chanu'tcristic impedance and that, over the range of frequencies necessary for the efficient transmission of speech, said characteristic impedance may be represented with a very high degree of precision by the following formula:

Z T /l 10 i'l o' il -21 1- 4;c(i clef This formula is identical with equation of my aborc-mentioned coqicndtng application, and the symbols have the same signiiicalico as follows: Z the characteristic impedance oi the periodically loaded line, a: Is the ratio oi the initial length of line up to the first load coil to the distance between load coils, and i denotes the imaginary operator T and-w are parameters havin the same significance as that assigned to t em in my copendlng application, viz:

In equations (4) and (5) sJ Q! table:

v 'w G 1. 0000 0529 9913 O900 9852 (6) .1369 9778 1936 9689 The above table includes the range of values of 71 found in practice, and for any particular value of r the corresponding value of w maybe readily obtained by interpolation therein. All of the foregoing equations are derived and explained in my above-mentioned co-pending a iplication.

Returning to equation (1) and writing I) and Q for the resistance and reactanco components of the characteristic impedance Z so that Z:D+2TQ, it follows at once that r zar n w g, (7)

Tau il ll vk Q I on L @10 (8) F m: w in terms of p, as given by equation. (3), and also substituting the value of T as given by equation (2), the

reduces to Now consider the rcactanre Q, of an inductance element L in. parallel with a capacity element (1,. The rcuctance of this arrangement is Well known to be expressible as:

may be made equal and opposite to Q by.

proportioning L and (1 so that Inspection of equation (11) shows that,

since all quantities therein are by their na ture necessarily positive, the relation expressed by said ,equation can only be satisfied values of w equal to or greater than 1/2. If, however an, the ratio of the length of the initial section to the length of each following section, is equal to or greater than 1/2 the combination of an inductance ele- Inent L and a, capacity element C in parallel, the values of said elements being proportioned in accordance with equations (11) and (12), has a rcactance equal and opposite to the characteristic reactance of a periodically loaded line characterized by the parameters L and (l As may be shown from the analysis appearing in my aforementioned co-pending application, this equality is of very high precision over substantially the entire range of frequencies corresponding to @0 20 to 10 :1, that is, over the range of frequencies necessary for the telephonic transmissimi of speech;

If now the impedance element having reactancc Q is prefixed to lhc periodically loaded line of characteristic impedance Z the impedance of the combination is obriously Z+iQ If, furfper, the component elements of Q, are proportioned in accordance with equations (11) and (12), then (3,: -Q., so that the impedance of the combination reduced to l) as given by equation ('i). Thus it is seen that the impedance of the combination has no reactance componcnt. D as given by equation (7) is a function of wi and, therefore, of the frequency, since w, is directly proportional to the frequency. The value of is proportional to the resistance conu'ionent,

, get the curve tioned by the cacao 20 :1; or, more accurately stated, to a little less than this range.

If now a: be taken as 0.8, equation (13) reduces to 211 T 1. 154w" and it from this equation we calculate the for different values of 10 from 0 to 1, and plot these values of 0 values of against the corresponding values of w we I own in Fig. d of the draw- It will is; noticed by reference to said Fig. 4 that the value of FF is approxiings.

mately constant and .losely equal to unity from w r-:0 to co l-.9. .The corresponding range of values Jf frequency are substantially those which are necessary for the telephonic transmission of speech. It should he noticed, however, that this constant resistance component characteristic is-c'ondichoice of a. particular value of w, namely about 0.8 and that for values of {B difi'ering materially from 0.8 this de sired characteristic does not hold. An ac tual loaded line does not of course begin in general with an 0.8 section; but it can always be built out artificially to a 0.8 initial section, as fully explained in my Patent #1,l2 4,904, dated January 12, 1915 and in myco-pending application; hereinbefore referred to.

If m is taken as 0.8 the values of L and (l, of the network of my invention become by aid of equations (11) and (12) To summarise the foregoing, the combination of a net .ork proportioned in accordunce with equations (11) and (12), and illustrated in Fig. l, prefixed to a pcriodically loaded line having an initial 'sectional length equal to approximately 0.8 of a loading section, has an impedance whose reactance component is substantially zero and whose resistance component is substantially constant and equal to T over the range of telephonic frequencies. The value of T is given by equation (2) above.

Referring to Fig. 1 of the accompany ng drawings, N is the network of my invent on comprising an. inductance L, ln parallel with a condenser the values of L, and C being those given by equations (15) and (16) of this specification. The actual numerical values of L, and C, depend on the values of L and 800, that is on the constants of the particular loaded line with winch it is desired to associate said network.

Referring to Fig. 2, 1 is a periodically loaded line having load coils 2, 2., 25, etc, inserted at regular intervals along the line. The distance betweenthe line terminals 3, 3 and the initial oad coil 2 is approximately 0.8 of the distaiiee between an two adjacent coils such as 2 and 2 or 2,, an 2,, fol'example. If the actual line does not have an initial 0.8 section it may be artificially built out to an equivalent 0.8 initial section as hereinbefore mentioned and fully ex lained in my abovementioned patent. Pre xed to terminals 3, 3 are similar and equal impedances 4, 4, each of said impedances comprising an nductance element 5, in parallel with a condenser 6. If the line 1 is characterized by the parameters L, and 800, then inductances 5, 5, and cbndensers 6, 6, are so proportioned that the inductance of inductance element 5 is 1/2L and the ca acity ofcondenser G is 20 where L and 6 are given by equations (15) and (16). The impedance of the two impedances 4, 4, in series is, therefore,the same as the impedance of the network N of Fig. 1. The reason for dividing the network into two equal parts, each having onehalf the impedance of the required network is to maintain the symmetr of the two sides of the transmission line an thereby to maintain its balance. From the theory developed in the specification it follows that the im' pedance of the combination seen from terminals 7, 7, will be substantially that of a constant non'inductive resistance of magnitude over the range of telephonic frequencies.

Referring to Fig. 3 the arrangement of Fig. 2 is connected throu h an autotransformer S to a. uniform 2.011- oaded line 9. lt will be understood that an equivalent transformer may replace the autotransformer ex .cept when conductive connection is desired. Terminals 7, 7 of the loaded line system are connected to terminals 10, 10 of transformer 8, while line 9 is connected to terminals 11, 11 of said transformer. If the nonloaded line has a distributed inductance J per unit length and a distributed capacity 0' per unit length is characteristic imped- ,ance is well known to be closely equal, ex-

cept for very low frequencies, to

Further if the transformer impedanceratio as seen irom terminals 11, 11 is r the appareat impedance of the loaded line system, as seen from terminals ll, 11, is substantially Hence if the transformer be so designed that iii Q; L /sU m the impedance of the entire system, as seen from terminals 12, 12, will be simply that is, the same as the impedance of an infinitely long uniform non-loaded line. As hereinbefore stated this is the condition for propagation without reflective losses.

The uses of my inrention are not limited to the cotiperativc arrangement illustrated. in Fig. 8, but my invention is applicable to any arrangement wherein it is desirable that a periodically loaded line shall have substantially no reactive impedance. As examples of further uses, my invention may be employed: (1) to connect a loaded-line type of filter to a repeater element whose impedance is a nearly constant resistance; (2) to connect a loaded line to a repeater system'whose impedancels nearly constant resistance; and (3) to connect a. loaded line to terminal apparatus whose impedance is a nearly constant resistance.

I do not desire to limit the proportioning of the network of my invention rigidly to formula: (11) and (12) or to values of .r exactly equal to 0.8. if very high precision is not necessary. I may, for instance. with small precision loss. proiortion L and C in accordance with the ['ollowing formula),

obtained by neglecting the. distributed inductance ol' the loaded line.

. L ::3L/l0 (l7) o sso ls (18) on the other hand, if extremely high procision is desired I may choose for w a value slightly different from 0.8; or I may compnte rigorously the impedance of an particular loaded line and then assign 3 and (l, values slightly different from those indicated by formulae (11) and (12) whereby the neutralization of reactance may be slightly more precise. in loaded lino systems it is customary and desirable to employ. two parallel and preferably similar circuits as the two sides of a third circuit called the phantom circuit. Three circuits are thus provided by means of four conductors, these circuits consisting of two side circuits and a phantom circuit. The current in each side circuit flows in opposite directions in the'two conductors of one line, while the current in the phantom 6s circuit tlows in the same direction in the ramp two conductors of a line. If the neutraliz ing network of my invention 18 to be at ployed in such a system to neutralize the ri active impedance of the two side circuits and of the phantom circuit, means must be provided whereby the neutralizing arrangements associated with'one circuit shall not afi'ect the transmission of current in the other circuits. Fig. 5 is a diagram of a reactance neutralizing arrangement de- 15 signed to be prefixed to such a'system and w ich shall satisfy the above-mentioned condition. Referring to Fig. 5, the terminals 20, 21 are connected to the two'sides 22, 23 of a loaded line 24; similarly terminals 20', 21' are connected to the two sides 22, 23 of a parallel loaded line 24. Conductors 22 and in parallel servt IS one side of the phantom circuit, of which the other side is composed of conductors 2'2 and 23 in parallel, said 1phantom circuit being also periodically loat ed. Lines 24 and 24 are separately the side circuits of the system. Considering the side circuit 24, the network of my invention associated there 99 with is represented by an arrangement 25, comprising two similar and equal condensers 26, 26. and two similar and equal coils 27, 27 wound on a common magnetic core and prefierably as-closely coupled as possible. The two coils 27, 27 are so wound as to be rnctically non-inductive to equal currents owing in the same direction in conductors 22 and 23 while to current flowing in the 0' p0 site directions in conductors 22 and 23 t eir resultant inductance is L when L is comnted from the constants of line 24 as hereinefore explained.\ The capacity of each condenser 26, 26 is 2C It will be evident therefore that the network 25 offers to the side circuit current flowing in line 24 an imedance equal to that of the network N *of *ig. 1, provided, of course, that L, and C, are proportioned in accordance with the constants of line 24. It will be further. evident that network 25 ofl'ers practical! .no im-- pedance to the phantom current owing inconductors 22 and 23, since coils 27, 27 are non-inductive with respect to the phantom current and their resistance may be made as small as desired.

Network 25 is similar in its component parts to network 25, and is the neutraliziilgfi network of line 24'. The values of corn.

densers 26', 26 and inductance coils 27, 27"120 are of course, proportioned in accordance. with the constants of line 24'. In practice lines 24 and 24' are similar and equal in which case networks 25 and 25' are similar and equal. 112;:

The circuitarrangement 28 comprisin":f

The four inductance coils 30, 30, 30', 30 are wound on a common magnetic circuit and are so related thereto that coils 30 and 30 are non-inductive with respect to the side 5 circuit current in line 24 and coils 30' and 30' are non-inductive with respect to the side circuit current in line 24. Said our coils are so proportioned as to offer a resultant inductance to the phantom circuit current of L when L is computed in accord ance with the phantom circuit constants. The capacity of each of the condensers 29, 29, 29', 29' is C when G, is computed in acoordance'with the phantom circuit constants. It will be evident then, that as regards the phantom circuit, the circuit arrangement 28 is equivalent to the network K of Fig. 1, and that further its insertion in the circuit will not appreciably affect the 9 transmission of the side circuit currents. It will be also observed that the inductance coils of Fig. are wound and related in substantially the same manner as are the load coils in a four wire transmission system comprising two loaded. side circuits and a loaded hantom circuit.

It wi 1 be understood that it is not necessary to combine the entire arrangement of Fig. 5 in a single organization; for olample if the phantom circuit is non-loaded while the side circuits are loaded, the network 28 is omitted. It should 'be further observed that while I have shown the network of my invention as proportioned in accordance with an actual loaded line, it may be more simply and exactly proportioned to neutralize the reactance of an artificial loaded line, since the two lines differ only in that the efl'ect of distributed induc ance is absent in the latter.

Claims:

1. A network for neutralizing the characteristic renctance of a periodically loaded signaling line, said network comprising precomputed impedance elements so proportioned in accordance with the constants of said line that the reactance of said network is substantially equal and opposite to the characteristic reactance of said line.

secutive load coils and the distributed capacity -and inductance of sand line.

2., A network for neutralizing the char- 4. A network having a reactance substantially equal and opposite to the characteristic reactance of a periodically loaded signaling line, said network co ising an inductance coil in parallel with condenser, the values of the inductance of said coil and the capacity of said condenser being precomputed in accordance with the load coil inductance, the distance between consecutive load coils and the distributed capacity and inductance of said loaded line.

5. In a telephone system, the combination of a periodically loaded transmission line and a network in series therewith. said network consisting of inductance and capacity elements so proportioned in accordance with the constants of said loaded line that the impedance of said combination is a practically pure constant resistance over the range of frequencies necessary for the transmission of speech.

6 in a telephone system. the combination of two parallel transmission lines constituting two side circuits and a phantom circuit, said circuits being periodically loaded, and a plurality of networks connected therewith, said networks including impedance elements so proportioned that the reactance of each of said circuits is substantially neutralized.

7. In a telephone system, the combination of two parallel transmission lines constituting two side circuits and a phantom circuit, said lines being periodically loaded as regards each side circuit and also as regards said phantom circuit, with two similar and equal networks in series with each of said side circuits respectively, each of said networks including precomputed inductance coils and condensers so proportioned in accordance with the constants of said side circuits and said phantom circuit that the impedance of the combination as seen from each of said side circuits and from said phantom 'circuit is approximately a. pure non-inductive resistance.

8. In a telephone system four parallel condoctors constituting two separate transmis sion lines and providing two side circuits and one phantom circuit, said conductors being periodically loaded as regards each sldo circuit and also as regards the phantom circuit, each of said conductors including two condensers in series, and an inductance coil shunting each of said condensers, the said inductance coils being so related as regards their mutual inductances and said inductance coils and said condensers being so proportioned in accordance with the constants of the periodically loaded side circuits and the periodically loaded phantom circuit that the characteristic impedance of each side circuit and of the phantom circuit is substantially a pure resistance.

9. The combination of a loaded line comprising lumped series inductance and shunt capacity in series with a network comprising an inductance coil in parallel with a. condenser. said network having a reactance substantially equal and opposite to that of said loaded line. and the values of the inductance of said inductance coil and the capacity of said condenser being proportioned in accordance with the inductance and rapzn'ity of said loaded line.

10. telephone circuit comprising a plurality oi wunhn-lors through which current flows in series and in parallel, and a conductive m-tuork included in each 01 the corn din-tow. said 114-! works being adapted to neull'ulizv llw l't'HlUlHCO of the circuit to current flow in one direction and cooperating with one another in prevent such neutralization for current flow in the other direction.

1!. telephone circuit comprising; a plu' mm;- of conductors, and a conductive netml; associated with each of the conductors, (:V'll 1101 work including branches containing impvdanccs of different character, imped- :lhw's of the same character in diiferent networks being tive relation.

12. A telephone circuit r litg of conductors, and a network consisting of a plurality of bramhes included in each conductor, with the branches of the networks of different conductors having inductance elements in mutually inductive relaiion.

l3. A telephone circuit comprising a plurality of conductors, and a network included in each of the conductors and consisting of a. branch containing an inductance element and a branch containing a capacity element, the inductance elements of the networks bein; in mutually inductive relation.

In testimony whereof, I have signed my name to this specification in the presence of two subscribing witi'iesses, this th day of January, 1916.

RAY S. HOYT. Witnesses FREDK S. ROBINSON, RALPH W. VVoLF.

arranged in mutually induccomprising a plu- 

